The invention relates to a pad for covering the upper surface of an air bag device that is installed to the steering wheel, the instrument panel in front of the assistant driver's seat of an automobile and the side door against the side collision. More particularly, the invention is directed to a pad for an air bag device, which is a highly productive single-layered molded body made of a thermoplastic elastomer (hereinafter referred to as "TPE").
Acronyms of major polymers used herein are listed below.
TPE . . . Thermoplastic elastomer PA1 PP . . . Polypropylene PA1 EPM . . . Amorphus ethylene-propylene random copolymer PA1 TPS . . . Styrene-containing TPE PA1 H-SBR . . . Hydrogenated styrene-butadiene copolymer PA1 SEBS . . . Styrene-ethylene-butylene-styrene block copolymer PA1 SEPS . . . Styrene-ethylene-propylene-styrene block copolymer
Conventionally, pads for covering air bag devices have usually been manufactured from polyurethane foams using reactive injection molding (RIM) techniques, with the foam being injection-molded with a net insert embedded therein. The net insert serves to reinforce the upper wall portion of the pad when the air bag is operated.
This conventional method, however, suffered from problems including: (1) the use of the net insert requires the net insert be set in the mold, which in turn increases the number of manufacturing steps; and (2) since polyurethanes used in RIM are thermosetting, the material cannot be reused
To overcome these problems, a pad for an air bag device molded in a single layer using a resin/elastomer blend was proposed, e.g., in Unexamined Japanese Patent Publication Nos. Hei. 4-314648 and Hei. 5-38996 Olefin resins and stylene elastomer were suggested therein as the resin and the elastomer.
However, the thus constructed pads are made soft considering the fact that the material becomes brittle at a low temperature (usually at -40.degree. C.).
As a result, not only the decorative part is easy to become sticky, but also abrasion resistance as well as weatherability are not sufficient, thus making it necessary to paint the decorative part before installation in an automobile.